Fasteners such as nails and staples are commonly used in projects ranging from crafts to building construction. While manually driving such fasteners into a work piece is effective, a user may quickly become fatigued when involved in projects requiring a large number of fasteners and/or large fasteners to be driven into a work piece. Moreover, proper driving of larger fasteners into a work piece frequently requires more than a single impact from a manual tool.
In response to the shortcomings of manual driving tools, power-assisted devices for driving fasteners into work pieces have been developed. Contractors and homeowners commonly use such devices for driving fasteners ranging from brad nails used in small projects to common nails which are used in framing and other construction projects. Compressed air has been traditionally used to provide power for the power-assisted (pneumatic) devices. However, other power sources have also been used, such as electric motors.
Various safety features have been incorporated into pneumatic and other power nailers. One such device is commonly referred to as a work contact element (WCE). A WCE is incorporated into nail gun designs to prevent unintentional firing of the nail gun. A WCE is typically a spring loaded mechanism which extends forwardly of the portion of the nail gun from which a nail is driven. In operation, the WCE is pressed against a work piece into which a nail is to be driven. As the WCE is pressed against the work piece, the WCE compresses the spring and generates an axial movement which is transmitted to a trigger assembly. The axial movement is used to reconfigure a safety device, also referred to as a trigger disabling mechanism, so as to enable initiation of a firing sequence with the trigger of the nail gun.
In past nailers incorporating a WCE, the safety mechanism has required two switches or sensors in order to operate. The first switch is coupled to the WCE and is closed only when the WCE is pressed against a work piece. In some existing nailers, the nailer's electric drive motor begins rotating in response to the first switch being closed. A second switch is coupled to a trigger that the user pulls in order to fire the nailer. A control mechanism, usually an electronic circuit, activates the nailer only in response to both switches being closed simultaneously. In certain embodiments, the control mechanism is also capable of determining the order in which the two switches were closed. If the WCE switch is closed, followed by the trigger switch, then the nailer will fire, but if the trigger switch is closed first, followed by the WCE switch, the nailer will not fire.
Existing nailers have several disadvantages. First, they require multiple switches adapted to use in different parts of the nailer. This increases the cost of materials, the cost of manufacturing, and potentially reduces the nailer's reliability. Second, nailers using an electronic control mechanism must provide a constant supply of electrical power to the electronic control device in order to determine when the different switches were closed in order to operate the nailer safely. Third, in nailers where depressing the WCE causes an electric drive motor to rotate, the motor may run for longer periods of time while the WCE is depressed but the user does not actually fire a nail, wasting electrical power. In existing hand-held nailers using portable power sources like batteries, the inefficiencies stated above result in the nailer having to be taken out of service for recharging more often.
What is needed is a fastener device with a safety mechanism incorporating a WCE that operates safely, but may be manufactured using fewer parts than traditional nailers. What is further needed is a fastener that uses less electrical energy by operating an electric drive motor and electronic control mechanism only for a minimum length of time needed to properly fire a fastener.